From: Thomas Albers (talbers_at_binghamton.edu)
Date: Sat Apr 07 2012 - 16:44:35 CDT
Hello!
> We have a cluster consisting of 8 AMD Phenom II x4 computers with GTX
> 460 video card linked with SDR Infiniband,
..
Some timing results, all with the F1ATPase benchmark:
> NAMD 2.9b2, compiled w/ gcc 4.5.3, 32 cores: 0.065 s/step
> NAMD 2.8 Linux-x86_64-ibverbs-CUDA, 32 cores: 0.039 s/step
>
> be affected. It's only the CUDA version of NAMD 2.9 that shows this
> odd scaling behavior. What is going on?
What went on is that between NAMD 2.8 and 2.9 the method of assigning
threads to GPUs has changed.
NAMD 2.9b3-ibverbs-CUDA, 32 cores, invoked with +devices 0,0,0,0: 0.039 s/step
NAMD 2.9b3-ibverbs-CUDA, 32 cores, invoked with +devices 0,0: 0.048 s/step
NAMD 2.9b3-ibverbs-CUDA, 32 cores, invoked with +devices 0: 0.065 s/step
I would be interested to hear from the developers what the reason for
this change of default behaviour is, on what kind of hardware does it
improve performance.
Regards,
Thomas
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